Inside the tiny 800-square-foot apartment that Tamerlan Tsarnaev shared with his wife, Katherine Russell, and their daughter, was where prosecutors say he may have built at least part of the bombs he and his brother deployed.

Related Content

As the jury weighs the fate of Dzhokhar Tsarnaev, questions remain about the fate of Russell and what she knew and didn't know before the 2013 attack.

"How could someone be in that apartment and not know what was going on?" 5 Investigates' Karen Anderson asked former U.S. Attorney Michael Sullivan.

"Common sense would tell you you'd be hard pressed not to know something was going on," Sullivan replied.

Prosecutors said in their closing argument that "there was some trace explosives in the apartment in Cambridge." And FBI agents found tools, a pickle jar full of nails and receipts for other equipment that could have been used to make the bomb. Prosecutors say Tamerlan bought the pressure cookers that were turned into bombs, as well as the backpacks he and his brother used to carry them to the Marathon finish line.

What Russell may have done or known is not publicly known, because she didn't testify at her brother-in-law's trial.

Last summer 5 Investigates tracked down Russell and her daughter living with the Tsarnaevs' sister Ailina and her family. She's the same sister who was arrested for threatening to "put a bomb" on a romantic rival in New York City.

"Get lost, get lost," Ailina told Anderson.

Russell was also spending time with the bombers' other sister, Bella, at a laundromat in North Bergen, New Jersey, where they sat and talked.

"Did you warn your husband after you saw the pictures the FBI released?" Anderson said.

Last summer Russell's legal team told us they didn't know if she was still under investigation. Her attorneys didn't return calls from 5 Investigates for this story. Her father said from Rhode Island that Russell wasn't there and he hadn't spoken with her.

The FBI also wouldn't comment for this story, and a spokesperson for U.S. Attorney Carmen Ortiz didn't respond to a request for comment.

Sullivan believes if she were exonerated, the government would have announced that by now.

"The fact that they haven't made that pronouncement suggests lingering question on the part of the government, law enforcement and prosecutors in terms of how much did she really know and what level of participation did she have," Sullivan said.